I use xrandr for decreasing screen resolution, without needing
modifying modes.

Thanks for the tip - I wasn't aware of xrandr - but my reason for
wanting the 896x600 framebuffer mode is so I can run MOL at 896x600 &
switch to the console without first enlarging the window to 1280x854. I
think I need the framebuffer mode for this, compatible, for instance,
with fbset. I took a look at the xrandr manpage, but I don't think
it'll work for this.

Thanks anyway - & if anyone can even suggest how to look for this
framebuffer mode, I'd be so grateful!